The field of cutting and welding metals comprises a number of techniques, of which three of the most prominent are the oxygen-acetylene, electric-arc, and plasma arc techniques. In oxygen-acetylene (or "oxy-acetylene") welding, a high temperature flame is generated by the combustion of acetylene in oxygen and then used to melt and weld metals. In electric-arc ("arc") welding, an electric potential is established between a metal workpiece and an electrode which are maintained in sufficiently close proximity for an electric arc to form between the electrode and the workpiece. The heat generated by the arc welds the metals. Typically, the arc and the metal are shielded from the surrounding atmosphere--which would otherwise tend to contaminate the weld--by the flow of an "inert" gas that is maintained adjacent the arc. In plasma arc welding, an electric arc is again formed between an electrode and a metal workpiece, and a gas flow is similarly maintained, but under such conditions of rapid gas flow and gas composition that the gases, rather than undergoing combustion reactions, become ionized and form a plasma. Plasmas typically have much higher temperatures than either combustion flames or electric arcs and therefore are useful for sophisticated welding and cutting techniques, or for welding or cutting metals which can withstand the relatively lower temperatures produced by oxy-acetylene or electric-arc techniques.
Although plasma arc cutting is particularly useful for cutting at relatively rapid rates, the voltages required to generate and sustain a plasma arc are typically very high. For example, typical plasma arc torches require and use power supplies producing between about 250 and 400 volts. By comparison, common electric-arc techniques such as tungsten inert gas (TIG) techniques typically operate at voltages of less than 100 volts, and are regulated by industry standards to about 80 volts or less. The higher voltage required for plasma arc welding and cutting makes the equipment more expensive to obtain and operate and limits its corresponding availability and use.
Alternatively, electric-arc power supplies, although more widely available, less expensive, and easier to operate, generally provide only enough power for electric-arc techniques. In comparison to plasma arc techniques, electric-arc techniques are generally slower, and are limited to welding. Prior attempts have been made to produce plasma arcs using low voltage power supplies and pure argon as the arc gas. Such devices and methods have suffered from the poor cut quality provided by argon, from the inconvenient necessity of water cooling systems, and from the additional equipment required (such as a pilot arc connection) that can be difficult to obtain.
Accordingly, there are presently no techniques or equipment which can be used to obtain the advantages of plasma arc cutting while avoiding the necessity of using high operating voltages and the associated required power supplies and other equipment.